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Adult polyglucosan body disease is a leukodystrophy, meaning a disease that predominantly impacts the cells that normally surround and protect the nerve cells of the brain. Such cells are called glia, and the areas of the brain where they are most common is called white matter.
What Causes APBD?
Adult polyglucosan body disease is caused by a deficiency of the glycogen branching enzyme (GBE). As a result, white matter in the brain begins to degenerate, though tissue damage involving nerve cells directly may also occur.
Under the microscope, unusual inclusions called polyglucosan bodies may be found inside in both nerve cells and glia.
The disease is due to a mutation that is inherited in an autosomal recessive fashion, meaning that a generation or more may go without obvious symptoms. Autosomal recessive diseases may be harder to detect than those mutations in which parents and children always shown signs of the disease. A detailed history of the family’s health problem may be necessary to recognize the problem. The mutation is more common in those of Ashkenazi Jewish heredity.
What are Signs and Symptoms of APBD?
The signs and symptoms of APBD can vary widely, which can also make the disorder difficult to diagnosis. That said, classically patients develop symptoms as adults in their fourth to seventh decade of life, as opposed to the more common leukodystrophies that primarily impact children. Those symptoms usually include urinary incontinence, problems walking, a peripheral neuropathy, and cognitive impairment.
Other possible symptoms include clumsiness (ataxia) or symptoms that can mimic Parkinson’s disease or amyotrophic lateral sclerosis.
How do Doctors Diagnose APBD?
In addition to detailed questions about symptoms experienced by the patient and any family members, doctors may order a brain MRI. That will typically show white matter changes both in the cerebral hemispheres and the cerebellum, an area near the back and bottom of the brain. Late in the disease there may show tissue loss in the cerebellum, cerebral hemispheres, and even the spinal cord. Holes in the white matter, called cavitations, may also sometimes be present.
The disease can also be made by performing a test of the glycogen branching enzyme gene (GBE1). GBE activity in blood leukocytes or skin fibroblasts can also be measured. A peripheral nerve biopsy may be able to show the telltale polyglucosan bodies. Some reports have shown that a skin biopsy may also be useful.
How is APBD treated?
Unfortunately, there is no effective therapy for APBD. Some clinical studies have suggested a benefit of an anaplerotic diet, though this has not been well studied. A mouse model has recently been discovered, which may lead to further treatments. The main treatments are supportive, meaning that symptoms can be addressed and managed as they arrive, despite an inability to treat the underlying cause of those symptoms. Because the disease is genetic, this disorder has implications for family members as well. Genetic counseling is recommended for all family members who want to discuss their risk of developing or spreading the disease, preferably before genetic testing is even performed.
Sources:
- Gray F, Gherardi R, Marshall A, et al. Adult polyglucosan body disease (APBD). J Neuropathol Exp Neurol. 1988;47(4):459-74.
- Klein CJ, Boes CJ, Chapin JE, et al. Adult polyglucosan body disease: case description of an expanding genetic and clinical syndrome.Muscle Nerve. 2004;29(2):323-8.
- Raben N, Danon M, Lu N, et al. Surprises of genetic engineering: a possible model of polyglucosan body disease. Neurology. 2001;56: 1739-45.
- Roe CR, Bottiglieri T, Wallace M, et al. Adult Polyglucosan Body Disease (APBD): Anaplerotic diet therapy (Triheptanoin) and demonstration of defective methylation pathways. Mol Genet Metab. 2010;101(2-3):246-52.
- Tay SK, Akman HO, Chung WK, et al. Fatal infantile neuromuscular presentation of glycogen storage disease type IV. Neuromuscul Disord. 2004;14(4):253-60.
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